There are several ways to configure this, some of which are simpler or harder, but I think this was an interesting way to do it.
# mkdir -p /etc/systemd/system/docker.service.d # echo -e '[Service]\nEnvironment="HTTP_PROXY=http://[::1]:8080/"' > /etc/systemd/system/docker.service.d/http-proxy.conf
Reload configuration and restart the docker daemon
# systemctl daemon-reload # systemctl restart docker
Verify that docker is run with the new environment
# systemctl show --property Environment docker Environment=GOTRACEBACK=crash DOCKER_HTTP_HOST_COMPAT=1 HTTP_PROXY=http://[::1]:8080/